Insulation Displacement Screw Terminals

7,510

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About: Retired Tool Maker ( 1980 ) Retired Mechanical Engineer ( 2009 ) Full time Tinkerer

I am a Model Railroader and do a lot of electrical wiring. It is most important to be able to keep track of the various connections. Since it is a hobby, keeping the cost low saves money for more important things, like more trains! These Insulation Displacement Screw Terminal Strips allow connecting wires in several ways.

1) Direct one wire to another wire.

2) One wire to several branch wires.

3) One wire to ring terminals.

Step 1: Cross Section at Wires and Screw

There are many ways to connect low voltage wires. Some take trained skills like using solder. Others are easy, but the parts can get expensive quickly. Few offer an easy way to make multiple connections to a common conductor.

I was working with some PVC trim boards and thought they might make nice terminal strips. Here is a cross section through the connection between two wires connected by a hex head sheet metal screw. I did a test at 11 amps and the connection didn't show any signs of heating up. Most model railroad currents are much less.

So a wiring method that doesn't require stripping insulation off the wires. No hot soldering iron. Multiple ways to make connections. And changes are as easy as taking a screw back out.

Step 2: PVC Trim Boards

The PVC trim boards are available in various widths and are not expensive. Also the hex head sheet metal screws are available in boxes of 1000 are cheap. Making the grooves is a simple task on a table saw, or you could use a chop saw or a radial arm saw. I cut the grooves 1/4" deep and used #8 x 1/2" screws. The hex head screws used in HVAC ducts are very easy to drive with a nut driver. Also the smooth white surface is easy to mark on with a Sharpie Pen. You can even color code the grooves!

Step 3: In Use

Here is a photo from under the train table.

The left photo shows two strips. The top common terminal has one wire pushed in for the full length. The lower terminal has individual wire connections.

The right photo has one strip with the individual wires connected at left and the common connections on the right end. The common wire is wrapped in a serpentine pattern. I found this made a neater arrangement for the wires.

These terminals are 3/4" wide and only allow one screw. We found if the strip were 1.5" wide you could put in two or three screws for more wires.

Step 4: Thick and Thin Wires

While the saw cut was just right for 18GA wire, what can you do about thinner wires? I found that if you folded thin wires over until they were about the thickness of a thicker wire it would work fine.

I hope this idea is useful for your model railroad.

Please work carefully.

Carl.

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    27 Discussions

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    carl5blum

    8 weeks ago

    Hi Gang: I've tested the voltage drop over 10 screw connections. Used a 15 amp heater as a load at 120 volts. After 10 minutes the light extension cord I used was getting warm, but not the PVC terminals. My digital meters showed a 0.1 volt drop over the ten connections. I also used an analog ( needle ) volt meter and I could barely see the needle move. So I would say the connections are better than a cheap extension cord. Please remember, I'm only suggesting these PVC terminal strips for use at less than 20 volts. Best wishes, Carl.

    Photo 1) A clamp on Amp Meter showing 15 amps.

    Photo 2) The tested terminals. Eleven screws and the cheap white extension cord.

    IMG_1923.JPGIMG_1922.JPG
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    ALGR1

    2 months ago on Step 4

    Hello mister i think is 0% safe, as you know electricity create heat , with the time the heat will burn that peace off PVC the fire will burn your workshop, or home or your garage please dont't use it in your home please as you putting your family at risk thank you

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    RanT1ALGR1

    Reply 2 months ago

    Electric currents only produce heat when they flow through a resistance. If the resistance is near-zero, they will produce near-zero heat.

    You're right to raise a warning: it could be very dangerous to use this technique to wire up high voltages or circuits where very high currents might flow even at low voltages. Even a 12V car battery can generate enough heat to start a fire if you you put a short across its terminals. But, as Carl says, if you only use it for low voltages, and with power sources like plug-in "wall warts" that can't produce a lot of current, the risk of fire is essentially zero.

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    carl5blumALGR1

    Reply 2 months ago

    Hello Algr1: These terminal blocks are ONLY for low voltage ( below 12 volt ). I used a 120 volt heater only as a test to see the reaction to high current. I plan to do a second test to see the voltage drop at the connection. I'll report the results here. The intended use of these connections are for model train layouts where the power is only on when you are in the room. It would be interesting to see if a very high current could burn the connections loose. Thank you for your concern. Carl.

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    JohnC430carl5blum

    Reply 2 months ago

    Yeah, you can apply a voltage across the connection and gradually increase the current while monitoring the temp of the screw. when it reaches 10 deg C above ambient that is your current limit. From what i see here you can have 20 amps flowing without any appreciable temp increase.

    Thanks for sharing this really cool and excellent idea and also safe. those who worry about shorting by things falling should visualize this connected in a vertical position so anything falling will not stay on it.

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    JohnC430Jack of Most Trades

    Reply 2 months ago

    I like the handle Jack of most trades. i am Jack of some trades and master of none... :)

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    LeanDean

    2 months ago on Step 4

    Thanks, most of the commercial strips are quite expensive. This is an excellent alternative for low voltage applications.

    1 reply
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    JohnC430LeanDean

    Reply 2 months ago

    Yeah, a short strip of pvc or even wood mounted vertically and then some screws to connect the wires. very good idea.

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    JohnW51

    2 months ago

    Way cool! I put in my favorites. I really like the idea of making something myself instead of shelling out $$ for parts. Those terminal strips and crimp-on terminals add up in a hurry, and you really need to have special tools to do a good job of crimping the terminals for maximum strength and safety. Your system looks to be just as good. One question though: how well does it hold up to removing and replacing wires? Does the PVC board wear out after a few remove/replace cycles?

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    JohnC430JohnW51

    Reply 2 months ago

    the "special tools" i use for crimping is a good hammer. just put the crimp with the wires in it and slam it with a hammer. it makes as good or better connection than the actual crimper plier. If you are still uncomfortable with the joint then add solder to it after you have 'crimped' it

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    carl5blumJohnW51

    Reply 2 months ago

    Hello John: There is some damage when you remove a screw. I don't use a screw on the same spot twice, just move over a bit. The wire can be quite chewed up, so nip off the bad spot. I haven't had to replace a terminal board yet, but what the heck, it wouldn't cost much to replace anyway. Good luck, Carl.

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    carl5blumCburg1

    Reply 2 months ago

    Hello Mike:

    Can you give us some part numbers? I looked at DigiKey and they had 67K items for wiring. Thanks, Carl.

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    carl5blumCburg1

    Reply 2 months ago

    Nice terminals. But you need to strip the wires and there is less room to write on them. Safer too with recessed screws. Both have their advantages and minuses.

    Carl.

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    PentagridCburg1

    Reply 2 months ago

    Wago make some very cool temporary connectors - Bigclive did a video about them.

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    BrandonW86

    2 months ago

    This is a genius solution to a common problem I've encountered in several applications invovling multiple circuits joined in a single location. My only qualms about this method is the potential of having a short between screw heads from something falling off and contacting them, but a cover made from more PVC (or even a few strips of electrical tape) would solve this.

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    carl5blum

    2 months ago

    Hello: Here is a photo of Ruth Mountain, named after my Aunt that made sure there were always toy trains under the Christmas Tree for me. Carl.

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    rmelchiori

    2 months ago

    You just need to keep in mind that all of those screw heads are now conducting electricity and he mindful of shorting between them.